The increased complexity and precision requirements of mechanical products has enhanced the need for accurately producing and controlling the surface texture of the manufactured parts. Variations in the surface texture can influence a variety of performance characteristics of the part. The surface texture can affect the ability of the part to resist wear and fatigue; to assist or destroy effective lubrication; to increase or decrease friction and/or abrasion with cooperating parts; and to resist corrosion. As these characteristics may become critical under certain operation conditions, the surface texture can dictate the performance and integrity of the component.
Distinct surface textures may be achieved through a variety of processes including tumbling, vibrating, honing, lapping, polishing, turning, milling and grinding. Metal objects such as stainless steel and aluminum have been tumbled or vibrated to remove burrs, clean, burnish and color the workpiece.
To accomplish these results through the tumbling or vibrating process, the prior art has manipulated the tumbling or vibrating material, the speed and the duration of the working period. Typically, parts having a relatively small size in relation to the barrel are processed loose within the tumbling or vibratory material. However, in the tumbling process, workpieces having a relatively large size in relation to the centrifugal barrel are usually fixed within the barrel so that the workpiece is not damaged by contact with the barrel or other workpieces during the tumbling process. In addition, the prior art tumbling and vibratory processes have included both dry and wet processes, typically employing rotational speeds from 12-25 rpm for the tumbling process or high frequency oscillations in the vibrating process. The operating time, while governed by the amount of tumbling or vibrating action desired, ranges from 1-8 hours.
The application of surface texturing techniques is especially critical in the surfaces of vanes, such as those used in turbines, jet engines or turbomachinery. The vanes in these applications are employed at extremely high rotational speeds which produce substantial internal stresses and forces within the vane. Under these operating conditions, a defect in the surface texture may propagate to produce a fracture which may result in a failure of the vane. The failure of a vane during operating conditions results in an uncontrolled high velocity mass. Such an uncontrolled mass can inflict substantial damage to the surrounding structure and components, thereby rendering the entire unit inoperative, or severely damaged. Also, the surface texture may obscure or hide surface defects, thereby preventing detection of a flawed component. The use of flawed components substantially increases the risk of product fracture.
In addition, these vanes operate in high temperature environments which also induces stress on the vane. The operating temperature of the vane may be increased by the friction of the vane with the surrounding fluid, thereby further stressing the vane.
Although the general tumbling and vibrating processes are available, the vanes employed in jet aircraft engines are surface textured according to specifications set forth by the vane or engine manufacturer. The manufacturers require the finishing and refurbishment of blades in compliance with industry standard specifications. These specifications typically require that after the vane is milled, the surface is sanded with a belt sander. The edge radii are then hand blended to achieve an aerodynamic curvature. The vanes are shot peened and processed in a vibratory bowl for a period which may exceed 4 hours. In addition, an abrasive sand blasting prior to the vibratory bowl is also required by some manufacturers.
The processing of the vanes, as required by manufacturer's specifications, introduces a substantial risk to the integrity of the vanes. Specifically, the shot peening and vibratory bowl process tends to deform the surface in such a manner so as to hide surface cracks or defects. As these defects may later propagate into failures, the shot peening prevents an adequate quality control of the processed vanes. In addition, the vibratory bowl process typically induces damage to the leading or trailing edge of the vane in approximately 10-20% of the workpieces. If the damage to the vane is minimal, the vane is repaired by hand; however, if the damage is above a certain threshold, the entire vane must be discarded.
Further, as the vibratory bowl process typically lasts for 4 hours, the additional handling and processing necessary to satisfy the specifications is a time consuming and labor intensive process. In addition, the large amount of manual labor introduces a high percentage of inconsistent results. Further, the surface texture achieved by the specifications produces an undesirable resistance to a passing air flow, thereby increasing fuel consumption and operating temperature of the engine.
Therefore, a need exists for a non-degrading method and apparatus for surface texturing a vane. Further, a need exists for producing a surface texture which does not hide or conceal surface defects. The need also exists for a method which produces uniform and reproducible results without requiring substantial human intervention. The need exists for an apparatus and method for providing a vane with a surface texture which minimizes the resistance to fluid flow relative to the surface, thereby reducing operating temperatures and increasing efficiency of the vane. Finally, a need exists for a surface texturing process which does not require substantial processing times and materials.